1. Field of the Invention
The present invention relates to liquid crystal displays, and especially to a transflective fringe field switching liquid crystal display (FFS LCD).
2. Description of the Prior Art
Recently, liquid crystal displays have become widely used in computer and communication products such as notebooks, cell phones and personal digital assistants. This is largely due to the thinness, lightness, and low power consumption of liquid crystal displays. Usually a liquid crystal display needs a planar light source, such as a backlight module, to display images. The backlight module is the main power consuming component of the liquid crystal display. In order to reduce power consumption, reflective type liquid crystal displays have been developed. A reflective liquid crystal display uses natural light beams to provide a planar light source. However, conventional reflective liquid crystal displays have some limitations; for example, a long response time and a narrow view angle.
To resolve the above-mentioned problems, a reflective fringe field switching liquid crystal display (FFS LCD) is described in U.S. Pat. No. 6,583,842 issued on Jun. 24, 2003. As represented in FIG. 4, the FFS LCD 1 includes a first substrate 10, a second substrate 12, and a liquid crystal layer 11 interposed between the substrates 10, 12.
The first substrate 10 comprises a first glass sheet 101 and a first alignment film 102. The first alignment film 102 is adhered on one surface (not labeled) of the first glass sheet 101, the surface facing the liquid crystal layer 11.
The second substrate 12 comprises a second glass sheet 121, a common electrode 122, an insulating layer 123, a plurality of pixel electrodes 124, and a second alignment film 125. The second glass sheet 121, the common electrode 122, and the insulating layer 123 are stacked from bottom to top in the order. The pixel electrodes 124 are formed on the insulating layer 123, and are spaced apart from and parallel to each other. The common electrode 122 is uniformly formed on the second glass sheet 121, and is made of a high reflectivity metal such as aluminum. Therefore, the common electrode 122 functions as both an electrically conductive electrode and a reflector.
The reflective FFS LCD 1 can efficiently use natural light beams, due to the reflection of the common electrode 122. Thus power consumption is reduced. Also, the common electrode 122 and the pixel electrodes 124 are both formed on the second substrate 12, which provides a dense fringe electric field parallel to the second substrate 12. The fringe electric field yields a fast response time and a wide view angle.
However, when the ambient environment is dark, the reflection of ambient light by the common electrode 122 is limited. The visibility of the reflective FFS LCD display 1 is poor. Conversely, a transmission type liquid crystal display is disadvantageous when the ambient environment is bright.
An improved liquid crystal display which overcomes the above-mentioned problems and shortcomings is desired.